Yes, this is physics. In fact, it is a field so big that it is almost
its own science. This subject is called fluid dynamics. The reason it
was hard to find information is that flowing water is not an easy thing
to understand. You would think that it is not that difficult, but since
it deals with a liquid instead of a solid, everything becomes more
There is still friction in when water flows. That friction is
called "viscosity". The thicker a liquid is, the slower it moves.
That's why pancake syrup moves slowly across your plate while water
would move much faster.
You may think that the motion of the water is only to flow down
hill, but there is also something called Brownian Motion. That
basically means that even when you have a glass of water just sitting
on a table, the water inside is moving.
To see this, put a glass of water on a table and let it settle.
Then drop a single drop of food coloring into the water. You will see
that the color spreads out and eventually fills the whole glass. That's
because the water is moving inside the glass.
(republished on 07/31/06)